1. Technical Field
The present invention relates to a light emitting element and a process for producing the same.
2. Background Art
Light emitting elements, particularly electroluminescent elements (hereinafter often referred to as “EL element”) which are field-effect light emitting elements, can realize high-intensity luminescence at a low applied voltage and further have high durability and high service life and thus are utilized in displays and the like.
In the production of a light emitting element, a luminescent layer should be formed by patterning of one or a plurality of luminescent materials. A vacuum deposition method, an ink jet printing method or photolithography and the like have been proposed as a method for luminescent layer pattern formation using a luminescent material.
Unlike the vapor deposition requiring the use of a vacuum apparatus provided with a high-accuracy alignment mechanism and the ink jet printing requiring partitions indispensable to patterning, pretreatment of a base material, an ink jet recording layer and the like, the photolithography requires none of these treatments and equipment and can form luminescent layers relatively easily at a low cost. In particular, the photolithography, as compared with the vapor deposition and the ink jet printing, has received attention as a method that can enhance luminescence efficiency of the luminescent layer and the light take-out efficiency to realize high-definition pattern formation.
An example of a method for forming a plurality of luminescent layers (for example, luminescent layers for RGB color mixture) by conventional photolithography is proposed, for example, in Japanese Patent Laid-Open No. 170673/2002. This method will be described with reference to FIG. 1. FIG. 1 is a process diagram showing a method for forming a plurality of luminescent layers by conventional photolithography. This method starts with step (a) and ends with step (n).
A coating liquid for a luminescent layer is coated onto a substrate (FIG. 1(a)), and a photoresist layer is stacked onto the coating (FIG. 1(b)). Next, only an area where the first luminescent layer is to formed is masked with a photomask, and the other area is exposed to ultraviolet light (FIG. 1(c)). The assembly is developed with a photoresist developing solution and is then washed to remove the photoresist layer in its exposed area (FIG. 1(d)). Further, the coating layer in its areas on which the photoresist layer is not stacked is removed by etching or the like to provide a luminescent layer with the photoresist layer stacked thereon (FIG. 1(e)). The above steps are further repeated twice (FIG. 1(f) to (m)), whereby patterning of three kinds of luminescent layers (luminescent layers for RGB color mixture) can be carried out. Finally, the individual photoresist layers are stripped with a photoresist stripping liquid to form three types of luminescent layers (FIG. 1(n)).
In FIG. 1, step (f) and step (j) are steps in which a coating liquid for a luminescent layer is coated to form a coating and a photoresist layer is formed onto the coating. In steps (g) to (i) and steps (k) to (m), respectively, the second luminescent layer and the third luminescent layer are patterned, and these steps are the same as steps (c) to (e).
In the above-described conventional photolithography, however, in forming a plurality of luminescent layers, for example, as shown in FIG. 1, when the formation of the first luminescent layer (FIG. 1(e)) is followed by coating of a coating liquid for second luminescent layer formation (FIG. 1(f)), the first luminescent layer in its exposed area is eluted into the coating liquid for second luminescent layer formation and, consequently, this sometimes causes color mixing or thinning down of pixels.
Accordingly, the development of photolithography, which can reduce color mixing or thinning down of pixels and can rapidly form a plurality of luminescent layers at a low cost, has been desired.